<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box1{
            width: 0;
            height: 0;
            border: 10px solid red;
            border-color:  transparent transparent #bbffaa transparent;
            border-top: none;

        }
    </style>
</head>
<body>
    <h1>您的数据已经收到</h1>

    <div class="box1">

    </div>
</body>
</html>